Stunning news today from yet another probe into the leak of classified information, a Justice Department official has confirmed to NPR that retired Marine General James Cartwright has been told that he is a target of a federal investigation. It stems from disclosures about a U.S.-Israeli cyber attack on Iran's nuclear facilities. Before retiring in 2011, Cartwright was the second-highest officer in the military, vice chairman of the Joint Chiefs of Staff.

For more on this, we're joined by NPR's Tom Gjelten. And to be clear, Tom, General Cartwright has not been charged with anything. But what is the suspicion here? What exactly is the Justice Department investigating?

TOM GJELTEN, BYLINE: Robert, this goes back to that story of Stuxnet, you know, the computer virus that targeted a nuclear enrichment plant in Iran. The New York Times reporter David Sanger wrote an article about this attack last summer, in which he said the United States and Israel were behind that attack. He said it was a part of a continuing cyber campaign targeting Iran. The program went by the name Olympic Games. And he had very detailed accounts of the White House discussions about the program, including quotes from participants in those discussions.

But it was a highly secret operation. The disclosure of a U.S. role caused an uproar. The Justice Department almost immediately launched an investigation. And, of course, we know this administration has been very aggressive in going after leakers. And now this word, first reported by NBC last night, that General Cartwright is a target.

SIEGEL: And was General Cartwright, in fact, a participant in those White House discussions that Sanger reported on?

GJELTEN: Indeed he was, Robert. He was vice chairman of the Joint Chiefs at the time. In fact, Sanger identified him as being a key player in the Olympic Games operation. But we should stress something important here. Sanger cites multiple sources in his story. I have his article here. He, for example, says in one case: According to members of the president's national security team who were in the room. So nothing in his reporting...

SIEGEL: Plural. Plural.

GJELTEN: Plural - nothing indicates that all this information came from one individual. We don't know who else is being investigated.

SIEGEL: It is remarkable that such a high-ranking officer would be suspected of, and being investigated for, a leak. Tell us about General Cartwright.

GJELTEN: He's a very smart guy. He was especially close to President Obama. In fact, David Sanger himself said that Obama saw him as one of his favorite strategists. He appeared to be in line to be chairman of the Joint Chiefs. But he had some disagreements with others in the Pentagon over Afghanistan policy. That may have cost him some support.

But I'll tell you, Robert, most of us who have covered national security issues have known General Cartwright. I have to say, my impression has always been that he's a real straight arrow. He certainly never leaked anything to me, Robert. He was always very careful in our conversations not to get into anything classified. So this is hard to understand.

SIEGEL: And, in fact, evidently his lawyer Gregory Craig - a very well-known Washington lawyer - released this statement late today.

(Reading) General Jim Cartwright is an American hero who served his country with distinction for four decades. Any suggestion that he could have betrayed the country he loves is preposterous.

The leak about Stuxnet is considered especially serious.

GJELTEN: Well, Stuxnet was the world's first cyber super weapon. And, you know, it was really a turning point in cyber war because it caused physical destruction. So it really was a stunner when the U.S. role in its creation was revealed.

SIEGEL: It's not about cyber spying. This was actually an attack on another country's...

GJELTEN: Like nothing before.

SIEGEL: Is there any indication of how this investigation led to General Cartwright?

GJELTEN: It's an important question, especially in the context of other leak investigations. You know, there is the Fox News reporter, for example, who had his email searched in an effort to find who gave him secret information. Did that happen in this case? We haven't heard yet from David Sanger or from The New York Times, so we still - there's a lot to come on this story.